The prevalence of diabetic nephropathy,the leading cause of end-stage renal failure, has been rising over the past years; despite recent advances in the management of diabetic patients.We have previously shown that the susceptibility to develop progressive glomerulosclerosis varies between mouse strains as it does between different ethnic groups. We identified both sclerosis-prone (ROP) and sclerosis-resistant (C57BL/6) mouse strains, and found that mesangial cells from these strains respond differently to glucose. Our preliminary data show that different sub-populations exist among mesangial cells isolated from sclerosis prone mice. They are characterized by a different length in the d(CA) repeat in the MMP-9 promoter, which recently has been linked to the risk of developing diabetic nephropathy. Rather than using this dinucleotide repeat for linkage studies, we propose that it can be used as a marker for mesangial cell sub-populations. In ROP mesangial cells, we identified single cell clones with d(CA)20 and d(CA)24 repeats. After exposure to high glucose levels, all mesangial cells isolated from ROP mice contained the d(CA)24 dinucleotide repeat. No heterogeneity in the d(CA) dinucleotide repeat length was detected at baseline in mesangial cells isolated from sclerosis-resistant C57BL/6 mice, and no change was observed after exposure to high glucose levels. This led us to propose that in susceptible individuals, diabetes mellitus leads to the clonal expansion of one of the mesangial sub-populations responsible for progressive glomerulosclerosis, and that the length of the d(CA) repeat in the MMP-9 promoter is a suitable marker to distinguish the different sub-populations. We will test the hypothesis that exposure to high glucose levels leads to a clonal selection in mesangial cells cultured from sclerosis-prone ROP mice. We will analyze the differences in gene expression that characterize sub-populations of mesangial cells in low and high glucose levels. The long-term goal of our proposal is to characterize the role of clonal selection in glomerular disease, and identify new targets for screening, prevention, and intervention in the pathogenesis of diabetic nephropathy.